3'-Substituted 7-halogenoindirubins, a new class of cell death inducing agents

Mechanistic insight and structure activity relationship of isatin-based derivatives in development of anti-breast cancer agents

Breast cancer is most common in women and most difficult to manage that causes highest mortality and morbidity among all diseases and posing significant threat to mankind as well as burden on healthcare system. In 2020, 2.3 million women were diagnosed with breast cancer and it was responsible for 685,000 deaths globally, suggesting the severity of this disease. Apart from that, relapsing of cases and resistance among available anticancer drugs along with associated side effects making the situation even worse. Therefore, it is a global emergency to develop potent and safer antibreast cancer agents. Isatin is most versatile and flying one nucleus which is an integral competent and various anticancer agent in clinical practice and widely used by various research groups around the globe for development of novel, potent, and safer antibreast cancer agents. This review will shed light on the structural insights and antiproliferative potential of various isatin-based derivatives developed for targeting breast cancer in last three decades that will help researchers in design and development of novel, potent, and safer isatin-based antibreast cancer agents.

Theoretical characterization and biological activity investigation of indirubins, cyclin dependent kinases inhibitors

Up to now, significant research efforts have been directed towards investigating indirubin and its derivatives as potential candidates for developing new compounds with multiple biological activities. In the present work, natural indirubin and numerous of its chemical derivatives referred to as indirubins have been investigated computationally using DFT method with the B3LYP/6-311 + G(d,p) level of theory, in order to reveal structure- biological activity relationship. We started with a structural properties description. Results analysis indicated that extra interaction sites were provided through the set of substitutions in compounds (1): Indirubin-3'-monoxime, (2): Indirubin-5-sulfonic acid, (3): 5-Nitro-indirubinoxime, (4): 5'-OH-5-nitro-indirubinoxime (AGM130), (5): 7-Bromo-5'-carboxyindirubin-3'-oxime, and (6): 7 BIO and consequently, extra hydrogen bonds may be formed with the active sites of molecular targets, such as GSK-3, CDKs, and Aurora kinases, as well as the aryl hydrocarbon receptor. Subsequently, to get more information on the electronic properties of indirubin and its analogues, HOMO, LUMO, Egap, and further electronic parameters were carried out. The indirubin derivatives showed an easier interaction with its environment than indirubin, the parent compound. The UV-Visible spectra of indirubin and compounds 1-6 were also produced using TD-DFT with B3LYP functional and 6-311 + G(2d,p) basis set. The relationship between absorption and chemical structure is discussed. Two phototoxic brominated compounds showed important absorption spectra modifications. It was also found that the main absorption bands of all compounds derived from π→π*(HOMO→LUMO) transitions.Communicated by Ramaswamy H. Sarma.

The Fundamental Role of Oxime and Oxime Ether Moieties in Improving the Physicochemical and Anticancer Properties of Structurally Diverse Scaffolds

The present review explores the critical role of oxime and oxime ether moieties in enhancing the physicochemical and anticancer properties of structurally diverse molecular frameworks. Specific examples are carefully selected to illustrate the distinct contributions of these functional groups to general strategies for molecular design, modulation of biological activities, computational modeling, and structure-activity relationship studies. An extensive literature search was conducted across three databases, including PubMed, Google Scholar, and Scifinder, enabling us to create one of the most comprehensive overviews of how oximes and oxime ethers impact antitumor activities within a wide range of structural frameworks. This search focused on various combinations of keywords or their synonyms, related to the anticancer activity of oximes and oxime ethers, structure-activity relationships, mechanism of action, as well as molecular dynamics and docking studies. Each article was evaluated based on its scientific merit and the depth of the study, resulting in 268 cited references and more than 336 illustrative chemical structures carefully selected to support this analysis. As many previous reviews focus on one subclass of this extensive family of compounds, this report represents one of the rare and fully comprehensive assessments of the anticancer potential of this group of molecules across diverse molecular scaffolds.

Synthesis and antibacterial activity studies in vitro of indirubin-3'-monoximes

Multi-drug-resistant microbial pathogens are a serious global health problem. New compounds with antibacterial activity serve as good candidates for developing novel antibacterial drugs which is very urgent and important. In this work, based on the unique scaffold of indirubin, an active ingredient of traditional Chinese medicine formulation Danggui Luhui Wan, we synthesized 29 indirubin-3'-monoximes and preliminarily evaluated their antibacterial activities. The antibacterial activity results demonstrated that the synthesized indirubin-3'-monoximes 5a-5z and 5aa-5ad displayed good potency against S. aureus ATCC25923 (MIC = 0.4-25.6 μg mL-1). Among them, we found that the 5-F, 5-Cl and 7-CF3 substituted indirubin-3'-monoximes 5r, 5s and 5aa also showed better antibacterial efficiency for S. aureus (MICs up to 0.4 μg mL-1) than the prototype natural product indirubin (MIC = 32 μg mL-1). More importantly, indirubin-3'-monoxime 5aa has certain synergistic effect with levofloxacin against clinic multidrug-resistant S. aureus (fractional inhibitory concentration index: 0.375). In addition, relevant experiments including electron microscopy observations, PI staining and the leakage of extracellular potassium ions and nucleic acid (260 nm) have been performed after treating S. aureus with indirubin-3'-monoxime 5aa, and the results revealed that indirubin-3'-monoximes could increase the cell membrane permeability of S. aureus. Although indirubin-3'-monoxime 5aa showed some cytotoxicity toward SH-SY5Y cells relative to compounds 5r and 5s, the skin irritation test of male mice after shaving showed that compound 5aa at a concentration of 12.8 μg mL-1 had no toxicity to mouse skin, and it could be used as a leading compound for skin antibacterial drugs.

Pharmacological properties of indirubin and its derivatives

BACKGROUND

Indirubin is the main bioactive component of the traditional Chinese medicine Indigo naturalis and is a bisindole alkaloid. Multiple studies have shown that indirubin exhibits good anticancer, anti-inflammatory and neuroprotective properties.

METHODS

The purpose of this review is to provide a summary of the pharmacological mechanisms of indirubin and its derivatives.

RESULTS

Indirubin and its derivatives exert anticancer effects by regulating the expression of cyclin-dependent kinases (CDKs), GSK-3β, Bax, Bcl-2, C-MYC, matrix metalloproteinases (MMPs), and focal adhesion kinase (FAK) through the PI3K/AKT/mTOR, nuclear factor (NF)-κB, mitogen-activated protein kinase (MAPK), JAK/signal transducer and activator of transcription 3 (STAT3) pathways and other signaling pathways. We also reviewed the anti-inflammatory and neuroprotective properties of indirubin and its derivatives.

CONCLUSION

The findings of recent studies assessing indirubin and its derivatives suggest that these compounds can be used as potential drugs to treat tumors, inflammation, neuropathy and bacterial infection.

Indirubin Derivatives as Dual Inhibitors Targeting Cyclin-Dependent Kinase and Histone Deacetylase for Treating Cancer

To utilize the unique scaffold of a natural product indirubin, we herein adopted the strategy of combined pharmacophores to design and synthesize a series of novel indirubin derivatives as dual inhibitors against cyclin-dependent kinase (CDK) and histone deacetylase (HDAC). Among them, the lead compound 8b with remarkable CDK2/4/6 and HDAC6 inhibitory activity of IC₅₀ = 60.9 ± 2.9, 276 ± 22.3, 27.2 ± 4.2, and 128.6 ± 0.4 nM, respectively, can efficiently induce apoptosis and S-phase arrest in several cancer cell lines. In particular, compound 8b can prevent the proliferation of a non-small-cell lung cancer cell line (A549) through the Mcl-1/XIAP/PARP axis, in agreement with the unique modes of action of the combined agents of HDAC inhibitors and CDK inhibitors. In an A549 xerograph model, compound 8b showed significant antitumor efficacy correlated with its dual inhibition. Our data demonstrated that compound 8b as a single agent could be a promising drug candidate for cancer therapy in combination with CDK and HDAC inhibitors.

Anticancer potential of indirubins in medicinal chemistry: Biological activity, structural modification, and structure-activity relationship

Indirubin is the crucial ingredient of Danggui Longhui Wan and Qing-Dai, traditional Chinese medicine herbal formulas used for the therapy of chronic myelocytic leukemia in China for hundreds of years. Although the monomeric indirubin has been used in China for the treatment human chronic myelocytic leukemia. However, due to low water solubility, poor pharmacokinetic properties and low therapeutic effects are the major obstacle, and had significantly limited its clinical application. Consequently, the attractive anticancer profile of indirubin has enthused numerous researchers to discover novel indirubin derivatives with improved pharmacodynamic activity as well as good pharmacokinetic property. In this paper, we comprehensively review the recent progress of anticancer potential of indirubins, structural modification and structure-activity relationship, which may provide useful direction for the further development of novel indirubins with improved pharmacological profiles for the treatment of various types of cancer.

Three-Component One-Pot Synthesis of Highly Functionalized Bis-Indole Derivatives

In this study, we detail the development of a concise and efficient three-component protocol for the regioselective synthesis of highly functionalized bis-indoles through a one-pot, two-step sequential process starting from enaminones 1, indoles 2, and acenaphthylene-1,2-dione 3 that is catalyzed by piperidine and p-methyl benzenesulfonic acid. This protocol has several advantages including simplicity of experimental operation, high efficiency of bond formation, ready availability and low cost of starting materials, environmentally benign conditions, and target molecular diversity.

Indirubin Analogues Inhibit Trypanosoma brucei Glycogen Synthase Kinase 3 Short and T. brucei Growth

The protozoan parasite Trypanosoma brucei is the causative agent of human African trypanosomiasis (HAT). The disease is fatal if it remains untreated, whereas most drug treatments are inadequate due to high toxicity, difficulties in administration, and low central nervous system penetration. T. brucei glycogen synthase kinase 3 short (TbGSK3s) is essential for parasite survival and thus represents a potential drug target that could be exploited for HAT treatment. Indirubins, effective leishmanicidals, provide a versatile scaffold for the development of potent GSK3 inhibitors. Herein, we report on the screening of 69 indirubin analogues against T. brucei bloodstream forms. Of these, 32 compounds had potent antitrypanosomal activity (half-maximal effective concentration = 0.050 to 3.2 μM) and good selectivity for the analogues over human HepG2 cells (range, 7.4- to over 641-fold). The majority of analogues were potent inhibitors of TbGSK3s, and correlation studies for an indirubin subset, namely, the 6-bromosubstituted 3'-oxime bearing an extra bulky substituent on the 3' oxime [(6-BIO-3'-bulky)-substituted indirubins], revealed a positive correlation between kinase inhibition and antitrypanosomal activity. Insights into this indirubin-TbGSK3s interaction were provided by structure-activity relationship studies. Comparison between 6-BIO-3'-bulky-substituted indirubin-treated parasites and parasites silenced for TbGSK3s by RNA interference suggested that the above-described compounds may target TbGSK3s in vivo To further understand the molecular basis of the growth arrest brought about by the inhibition or ablation of TbGSK3s, we investigated the intracellular localization of TbGSK3s. TbGSK3s was present in cytoskeletal structures, including the flagellum and basal body area. Overall, these results give insights into the mode of action of 6-BIO-3'-bulky-substituted indirubins that are promising hits for antitrypanosomal drug discovery.

Indirubin derivatives are potent and selective anti-Trypanosoma cruzi agents

Current treatment for combatting Chagas disease, a life-threatening illness caused by the kinetoplastid protozoan parasite Trypanosoma cruzi is inadequate, and thus the discovery of new antiparasitic compounds is of prime importance. Previous studies identified the indirubins, a class of ATP kinase inhibitors, as potent growth inhibitors of the related kinetoplastid Leishmania. Herein, we evaluated the inhibitory activity of a series of 69 indirubin analogues screened against T. cruzi trypomastigotes and intracellular amastigotes. Seven indirubins were identified as potent T. cruzi inhibitors (low μΜ, nM range). Cell death analysis of specific compounds [3'oxime-6-bromoindirubin(6-BIO) analogues 10, 11 and 17, bearing a bulky extension on the oxime moiety and one 7 substituted analogue 32], as evaluated by electron microscopy and flow cytometry, showed a different mode of action between compound 32 compared to the three 6-BIO oxime- substituted indirubins, suggesting that indirubins may kill the parasite by different mechanisms dependent on their substitution. Moreover, the efficacy of four compounds that show the most potent anti-parasitic effect in both trypomastigotes and intracellular amastigotes (10, 11, 17, 32), was evaluated in a mouse model of T. cruzi infection. Compound 11 (3ʹpiperazine-6-BIO) displayed the best in vivo efficacy (1/6 mortality, 94.5% blood parasitaemia reduction, 12 dpi) at a dose five times reduced over the reference drug benznidazole (20 mg/kg vs100 mg/kg). We propose 3ʹpiperazine-6-BIO as a potential lead for the development of new treatments of Chagas disease.

Isatin and its derivatives: a survey of recent syntheses, reactions, and applications

Isatin (1H-indole-2,3-dione) and its derivatives represent an important class of heterocyclic compounds that can be used as precursors for drug synthesis. Since its discovery, a lot of research work has been done regarding the synthesis, chemical properties, and biological and industrial applications of isatin. In this review, we have reported several novel methods for the synthesis of N-, C2-, and C3-substituted and spiro derivatives of isatin. The isatin moiety also shows important chemical reactions such as oxidation, ring expansion, Friedel-Crafts reaction and aldol condensation. These reactions, in turn, produce several biologically viable compounds like 2-oxindoles, tryptanthrin, indirubins, and many more. We have also summarized some recently reported biological activities exhibited by isatin derivatives, like anti-cancer, anti-bacterial, anti-diabetic and others. Special attention has been paid to their anti-cancer activity, and various anti-cancer targets such as histone deacetylase, carbonic anhydrase, tyrosine kinase, and tubulin have been discussed in detail. Other applications of isatin derivatives, such as in the dye industry and in corrosion prevention, have also been discussed.

Effects of indirubin and isatin on cell viability, mutagenicity, genotoxicity and BAX/ERCC1 gene expression

CONTEXT

Indigofera suffruticosa Miller (Fabaceae) and I. truxillensis Kunth produce compounds, such as isatin (ISA) and indirubin (IRN), which possess antitumour properties. Their effects in mammalian cells are still not very well understood.

OBJECTIVE

We evaluated the activities of ISA and/or IRN on cell viability and apoptosis in vitro, their genotoxic potentials in vitro and in vivo, and the IRN- and ISA-induced expression of ERCC1 or BAX genes.

MATERIALS AND METHODS

HeLa and/or CHO-K1 cell lines were tested (3 or 24 h) in the MTT, Trypan blue exclusion, acridine orange/ethidium bromide, cytokinesis-blocked micronucleus (CBMN) and comet (36, 24 and 72 h) tests after treatment with IRN (0.1 to 200 μM) or ISA (0.5 to 50 μM). Gene expression was measured by RT-qPCR in HeLa cells. Swiss albino mice received IRN (3, 4 or 24 h) by gavage (50, 100 and 150 mg/kg determined from the LD₅₀ - 1 g/kg b.w.) and submitted to comet assay in vivo.

RESULTS

IRN reduced the viability of CHO-K1 (24 h; 5 to 200 μM) and HeLa cells (10 to 200 μM), and was antiproliferative in the CBMN test (CHO-K1: 0.5 to 10 μM; HeLa: 5 and 10 μM). The drug did not induce apoptosis, micronucleus neither altered gene expression. IRN and ISA were genotoxic for HeLa cells (3 and 24 h) at all doses tested. IRN (100 and 150 mg/kg) also induced genotoxicity in vivo (4 h).

CONCLUSION

IRN and ISA have properties that make them candidates as chemotherapeutics for further pharmacological investigations.

Inhibition mechanism of CDK-2 and GSK-3β by a sulfamoylphenyl derivative of indoline-a molecular dynamics study

A good understanding of the inhibition mechanism of enzymes exhibiting high levels of similarity is the first step to the discovery of new drugs with selective potential. Examples of such proteins include glycogen synthase kinase-3 (GSK-3β) and cyclin-dependent kinase 2 (CDK-2). This article reports the mechanism of such enzyme inhibition as analyzed by an indoline sulfamylophenyl derivative (CHEMBL410072). Previous work has shown that such compounds exhibit selective properties towards their biological targets. This study used a combined procedure involving docking and molecular dynamics simulations, which allowed identification of interactions responsible for stabilization of complexes, and analysis of the dynamic stability of the systems obtained. The initial data obtained during the molecular docking stage show that the ligand molecule exhibits a similar affinity towards both active sites, which was confirmed by quantification of identified interactions and energy values. However, the data do not cover dynamic aspects of the considered systems. Molecular dynamics simulations realized for both complexes indicate significant dissimilarities in dynamics properties of both side chains of the considered ligands, especially in the case of the part containing the sulfamide group. Such increased mobility of the analyzed systems disrupts the stability of binding in the stabilized complex with GSK-3β protein, which finally affects also the binding affinity of the ligand molecule towards this enzyme.

Natural-Based Indirubins Display Potent Cytotoxicity toward Wild-Type and T315I-Resistant Leukemia Cell Lines

Drug resistance in chronic myelogenous leukemia (CML) requires the development of new CML chemotherapeutic drugs. Indirubin, a well-known mutikinase inhibitor, is the major active component of "Danggui Longhui Wan", a Chinese traditional medicine used for the treatment of CML symptoms. An in-house collection of indirubin derivatives was screened at 1 μM on wild-type and imatinib-resistant T315I mutant CML cells. Herein are reported that only 15 analogues of the natural 6-bromoindirubin displayed potent cytotoxicity in the submicromolar range. Kinase assays in vitro show that eight out of the 15 active molecules strongly inhibited both c-Src and Abl oncogenic kinases in the nanomolar range. Most importantly, these eight molecules blocked the activity of T315I mutant Abl kinase at the submicromolar level and with analogue 22 exhibiting inhibitory activity at the low nanomolar range. Docking calculations suggested that active indirubins might inhibit T315I Abl kinase through an unprecedented binding to both active and Src-like inactive conformations. Analogue 22 is the first derivative of a natural product identified as an inhibitor of wild-type and imatinib-resistant T315I mutant Abl kinases.

From Drug Screening to Target Deconvolution: a Target-Based Drug Discovery Pipeline Using Leishmania Casein Kinase 1 Isoform 2 To Identify Compounds with Antileishmanial Activity

Existing therapies for leishmaniases present significant limitations, such as toxic side effects, and are rendered inefficient by parasite resistance. It is of utmost importance to develop novel drugs targeting Leishmania that take these two limitations into consideration. We thus chose a target-based approach using an exoprotein kinase, Leishmania casein kinase 1.2 (LmCK1.2) that was recently shown to be essential for intracellular parasite survival and infectivity. We developed a four-step pipeline to identify novel selective antileishmanial compounds. In step 1, we screened 5,018 compounds from kinase-biased libraries with Leishmania and mammalian CK1 in order to identify hit compounds and assess their specificity. For step 2, we selected 88 compounds among those with the lowest 50% inhibitory concentration to test their biological activity on host-free parasites using a resazurin reduction assay and on intramacrophagic amastigotes using a high content phenotypic assay. Only 75 compounds showed antileishmanial activity and were retained for step 3 to evaluate their toxicity against mouse macrophages and human cell lines. The four compounds that displayed a selectivity index above 10 were then assessed for their affinity to LmCK1.2 using a target deconvolution strategy in step 4. Finally, we retained two compounds, PP2 and compound 42, for which LmCK1.2 seems to be the primary target. Using this four-step pipeline, we identify from several thousand molecules, two lead compounds with a selective antileishmanial activity.

Isatin derivatives with activity against apoptosis-resistant cancer cells

In a search of small molecules active against apoptosis-resistant cancer cells, a series of isatin-based heterocyclic compounds were synthesized and found to inhibit proliferation of cancer cell lines resistant to apoptosis. The synthesis of these compounds involved a condensation of commercially available, active methylene heterocycles with isatin proceeding in moderate to excellent yields. The heterocyclic scaffolds prepared in the current investigation appear to be a useful starting point for the development of agents to fight cancers with apoptosis resistance, and thus, associated with dismal prognoses.

Ru-Catalyzed selective C–H oxidative olefination with N-heteroarenes directed by pivaloyl amide

Ruthenium-catalysed C7-position alkynylation for indoline derivatives with various olefins was reported.

Induction of atypical cell death in thyroid carcinoma cells by the indirubin derivative 7-bromoindirubin-3'-oxime (7BIO)

BACKGROUND

The indirubin derivative 7-bromoindirubin-3'-oxime (7BIO) has already shown anticancer properties by causing cell death in some tumour cell lines and may be a new therapeutic option for treatment-resistant tumour cells. Since dedifferentiated and anaplastic thyroid carcinomas do not take up radioiodine and are insensitive to chemotherapeutic treatment and external radiation, direct cell death induction in these tumour cells may be a promising approach. We thus investigated the effect of 7BIO on thyroid carcinoma cell lines of different histological origins and characterized the type of cell death induction by 7BIO.

METHODS

Cell viability was measured with MTT assay. Cell death was analysed by caspase 3/7 activity, lactate dehydrogenase liberation, caspase cleavage products, DNA fragmentation, cell cycle phase distribution and LC3B analysis.

RESULTS

After 7BIO treatment, cell viability was reduced in all 14 thyroid carcinoma cell lines investigated. Treated cells showed DNA fragmentation, cell cycle arrest and lactate dehydrogenase liberation but no LC3B cleavage. Caspase activation following 7BIO treatment was found in five of six cell lines investigated. Interestingly, inhibition of caspases had no effect on viability of the cells after 7BIO incubation.

CONCLUSIONS

Our results indicate that 7BIO efficiently killed dedifferentiated thyroid carcinoma cells. It induced a non-classical kind of cell death that was caspase-independent and includes DNA fragmentation. 7BIO and related indirubin components thus may have value as a new therapeutic option for dedifferentiated thyroid cancer irrespective of the exact target molecules and the kind of cell death they induce.

Indirubin and Indirubin Derivatives for Counteracting Proliferative Diseases

Indirubin is the active component of Danggui Longhui Wan, a traditional Chinese medicine formulation. The encouraging clinical results from the 1980s obtained in chronic myelocytic leukemia patients treated with indirubin stimulated numerous studies on this compound. These investigations explored the use of indirubin in different types of cancer and reported the synthesis of novel derivatives with improved chemical and pharmacokinetic properties. In this paper, we review the impressive progress that has been made in elucidating the mechanistic understanding of how indirubin and its derivatives affect physiological and pathophysiological processes, mainly by inhibition of cell proliferation and induction of cell death. Furthermore, we survey the therapeutic use of these compounds in combating proliferative diseases such as cancer, restenosis, and psoriasis.

An evaluation of indirubin analogues as phosphorylase kinase inhibitors

Phosphorylase kinase (PhK) has been linked with a number of conditions such as glycogen storage diseases, psoriasis, type 2 diabetes and more recently, cancer (Camus et al., 2012 [6]). However, with few reported structural studies on PhK inhibitors, this hinders a structure based drug design approach. In this study, the inhibitory potential of 38 indirubin analogues have been investigated. 11 of these ligands had IC50 values in the range 0.170-0.360μM, with indirubin-3'-acetoxime (1c) the most potent. 7-Bromoindirubin-3'-oxime (13b), an antitumor compound which induces caspase-independent cell-death (Ribas et al., 2006 [20]) is revealed as a specific inhibitor of PhK (IC50=1.8μM). Binding assay experiments performed using both PhK-holo and PhK-γtrnc confirmed the inhibitory effects to arise from binding at the kinase domain (γ subunit). High level computations using QM/MM-PBSA binding free energy calculations were in good agreement with experimental binding data, as determined using statistical analysis, and support binding at the ATP-binding site. The value of a QM description for the binding of halogenated ligands exhibiting σ-hole effects is highlighted. A new statistical metric, the 'sum of the modified logarithm of ranks' (SMLR), has been defined which measures performance of a model for both the "early recognition" (ranking earlier/higher) of active compounds and their relative ordering by potency. Through a detailed structure activity relationship analysis considering other kinases (CDK2, CDK5 and GSK-3α/β), 6'(Z) and 7(L) indirubin substitutions have been identified to achieve selective PhK inhibition. The key PhK binding site residues involved can also be targeted using other ligand scaffolds in future work.

Antiplatelet action of indirubin-3'-monoxime through suppression of glycoprotein VI-mediated signal transduction: a possible role for ERK signaling in platelets

We investigated the antiplatelet activity of indirubin-3'-monoxime (I3O) and the underlying mechanisms. In a rat carotid artery injury model, oral administration (20 mg/kg/day) of I3O for 3 days significantly prolonged occlusion time, and ADP- and collagen-induced platelet aggregation. In washed platelets in vitro, I3O potently inhibited collagen-induced platelet aggregation by suppressing phospholipase Cγ2 (PLCγ2) phosphorylation, subsequently blocking diacylglycerol and arachidonic acid (AA) formation, P-selectin secretion and the production of thromboxane B2. Platelet aggregation induced by phorbol-12-myristate 13-acetate, a protein kinase C (PKC) activator, was inhibited by I3O. Both I3O and U0126, an extracellular signal-regulated kinase 1/2 (ERK1/2) inhibitor, markedly reduced collagen-induced phosphorylation of ERK1/2 and p47, resulting in the blockade of cyclooxygenase (COX)-mediated AA metabolite production in AA-treated platelets. I3O suppressed phosphorylation of JNK, p38, GSK-3β, and AKT. I3O inhibited glycoprotein VI (GPVI), as a collagen receptor, by suppressing the phosphorylation of tyrosine kinase Syk of GPVI and the phosphorylation of PLCγ2 and ERK1/2 stimulated by convulxin, as a specific stimulator. Our results indicate that an antiplatelet effect of I3O is due to the suppression of GPVI-mediated signaling pathways. In collagen-stimulated platelets, ERK1/2 phosphorylation is adenylyl cyclase-dependent and leads to the modulation of PKC-p47 signaling and COX-1-mediated AA-metabolic pathways.

An inhibitor-driven study for enhancing the selectivity of indirubin derivatives towards leishmanial Glycogen Synthase Kinase-3 over leishmanial cdc2-related protein kinase 3

Background

In search of new antiparasitic agents for overcoming the limitations of current leishmaniasis chemotherapy, we have previously shown that 6-bromoindirubin-3'-oxime (6BIO) and several other 6-substituted analogues of indirubin, a naturally occurring bis-indole present in mollusks and plants, displayed reverse selectivity from the respective mammalian kinases, targeting more potently the leishmanial Cyclin-Dependent Kinase-1 (CDK1) homologue [cdc2-related protein kinase 3 (LCRK3)] over leishmanial Glycogen Synthase Kinase-3 (LGSK-3). This reversal of selectivity in Leishmania parasites compared to mammalian cells makes the design of specific indirubin-based LGSK-3 inhibitors difficult. In this context, the identification of compounds bearing specific substitutions that shift indirubin inhibition towards LGSK-3, previously found to be a potential drug target, over LCRK3 is imperative for antileishmanial targeted drug discovery.

Methods

A new in-house indirubin library, composed of 35 compounds, initially designed to target mammalian kinases (CDKs, GSK-3), was tested against Leishmania donovani promastigotes and intracellular amastigotes using the Alamar blue assay. Indirubins with antileishmanial activity were tested against LGSK-3 and LCRK3 kinases, purified from homologous expression systems. Flow cytometry (FACS) was used to measure the DNA content for cell-cycle analysis and the mode of cell death. Comparative structural analysis of the involved kinases was then performed using the Szmap algorithm.

Results

We have identified 7 new indirubin analogues that are selective inhibitors of LGSK-3 over LCRK3. These new inhibitors were also found to display potent antileishmanial activity with GI₅₀ values of <1.5 μΜ. Surprisingly, all the compounds that displayed enhanced selectivity towards LGSK-3, were 6BIO analogues bearing an additional 3'-bulky amino substitution, namely a piperazine or pyrrolidine ring. A comparative structural analysis of the two aforementioned leishmanial kinases was subsequently undertaken to explain and rationalize the selectivity trend determined by the in vitro binding assays. Interestingly, the latter analysis showed that selectivity could be correlated with differences in kinase solvation thermo dynamics induced by minor sequence variations of the otherwise highly similar ATP binding pockets.

Conclusions

In conclusion, 3'-bulky amino substituted 6-BIO derivatives, which demonstrate enhanced specificity towards LGSK-3, represent a new scaffold for targeted drug development to treat leishmaniasis.

MLS-2384, a new 6-bromoindirubin derivative with dual JAK/Src kinase inhibitory activity, suppresses growth of diverse cancer cells

Janus kinase (JAK) and Src kinase are the two major tyrosine kinase families upstream of signal transducer and activator of transcription (STAT). Among the seven STAT family proteins, STAT3 is constitutively activated in many diverse cancers. Upon activation, JAK and Src kinases phosphorylate STAT3, and thereby promote cell growth and survival. MLS-2384 is a novel 6-bromoindirubin derivative with a bromo-group at the 6-position on one indole ring and a hydrophilic group at the 3'-position on the other indole ring. In this study, we investigated the kinase inhibitory activity and anticancer activity of MLS-2384. Our data from in vitro kinase assays, cell viability analyses, western blotting analyses, and animal model studies, demonstrate that MLS-2384 is a dual JAK/Src kinase inhibitor, and suppresses growth of various human cancer cells, such as prostate, breast, skin, ovarian, lung, and liver. Consistent with the inactivation of JAK and Src kinases, phosphorylation of STAT3 was inhibited in a dose-dependent manner in the cancer cells treated with MLS-2384. STAT3 downstream proteins involved in cell proliferation and survival, such as c-Myc and Mcl-1, are downregulated by MLS-2384 in prostate cancer cells, whereas survivin is downregulated in A2058 cells. In these two cancer cell lines, PARP is cleaved, indicating that MLS-2384 induces apoptosis in human melanoma and prostate cancer cells. Importantly, MLS-2384 suppresses tumor growth with low toxicity in a mouse xenograft model of human melanoma. Taken together, MLS-2384 demonstrates dual JAK/Src inhibitory activity and suppresses tumor cell growth both in vitro and in vivo. Our findings support further development of MLS-2384 as a potential small-molecule therapeutic agent that targets JAK, Src, and STAT3 signaling in multiple human cancer cells.

QSAR study and molecular docking on indirubin inhibitors of Glycogen Synthase Kinase-3

The current study describes the development of in silico models based on a novel alternative of the MTD-PLS methodology (Partial-Least-Squares variant of Minimal Topologic Difference) developed by our group to predict the inhibition of GSK-3β by indirubin derivatives. The new MTD-PLS methodology involves selection rules for the PLS equation coefficients based on physico-chemical considerations aimed at reducing the bias in the output information. These QSAR models have been derived using calculated fragmental descriptors relevant to binding including polarizability, hydrophobicity, hydrogen bond donor, hydrogen bond acceptor, volume and electronic effects. The MTD-PLS methodology afforded moderate but robust statistical characteristics (R2 Y(CUM) = 0.707, Q2(CUM) = 0.664). The MTD-PLS model obtained has been validated in terms of predictive ability by joined internal-external cross-validation applying Golbraikh-Tropsha criteria and Y-randomization test. The information supplied by the MTD-PLS model has been evaluated against Fujita-Ban outcomes that afforded a statistically reliable model (R2=0.923). Furthermore, the results originated from QSAR models were laterally validated with docking insights that suggested the substitution pattern for the design of new indirubins with improved pharmacological potential against GSK-3β. The new restriction rules introduced in this paper are applicable and provide reliable results in accordance with physico-chemical reality.

A novel 7-bromoindirubin with potent anticancer activity suppresses survival of human melanoma cells associated with inhibition of STAT3 and Akt signaling

STAT3 and Akt signaling have been validated as potential molecular targets for treatment of cancers including melanoma. These small molecule inhibitors of STAT3 or Akt signaling are promising for developing anti-melanoma therapeutic agents. MLS-2438, a novel 7-bromoindirubin, a derivative of the natural product indirubin, was synthesized with a bromo-group at the 7-position on one indole ring and a hydrophilic group at the 3'-position on the other indole ring. We tested the anticancer activity of MLS-2438 and investigated its mechanism of action in human melanoma cell lines. Here, we show that MLS-2438 inhibits viability and induces apoptosis of human melanoma cells associated with inhibition of STAT3 and Akt signaling. Several pro-apoptotic Bcl-2 family proteins are involved in the MLS-2438 mediated apoptosis. MLS-2438 inhibits Src kinase activity in vitro and phosphorylation of JAK2, Src, STAT3 and Akt in cultured cancer cells. In contrast to the decreased phosphorylation levels of JAK2, Src, STAT3 and Akt, phosphorylation levels of the MAPK (Erk1/2) signaling protein were not reduced in cells treated with MLS-2438. These results demonstrate that MLS-2438, a novel natural product derivative, is a Src inhibitor and potentially regulates kinase activity of JAK2 and Akt in cancer cells. Importantly, MLS-2438 suppressed tumor growth with low toxicity in a mouse xenograft model of human melanoma. Our findings support further development of MLS-2438 as a potential small-molecule therapeutic agent that targets both STAT3 and Akt signaling in human melanoma cells.

Induction of discrete apoptotic pathways by bromo-substituted indirubin derivatives in invasive breast cancer cells

Indirubin derivatives gained interest in recent years for their anticancer and antimetastatic properties. The objective of the present study was to evaluate and compare the anticancer properties of the two novel bromo-substituted derivatives 6-bromoindirubin-3'-oxime (6BIO) and 7-bromoindirubin-3'-oxime (7BIO) in five different breast cancer cell lines. Cell viability assays identified that 6BIO and 7BIO are most effective in preventing the proliferation of the MDA-MB-231-TXSA breast cancer cell line from a total of five breast cancer cell lined examined. In addition it was found that the two compounds induce apoptosis via different mechanisms. 6BIO induces caspase-dependent programmed cell death through the intrinsic (mitochondrial) caspase-9 pathway. 7BIO up-regulates p21 and promotes G(2)/M cell cycle arrest which is subsequently followed by the activation of two different apoptotic pathways: (a) a pathway that involves the upregulation of DR4/DR5 and activation of caspase-8 and (b) a caspase independent pathway. In conclusion, this study provides important insights regarding the molecular pathways leading to cell cycle arrest and apoptosis by two indirubin derivatives that can find clinical applications in targeted cancer therapeutics.

6-Bromoindirubin-3'-oxime inhibits JAK/STAT3 signaling and induces apoptosis of human melanoma cells

STAT3 is persistently activated and contributes to malignant progression in various cancers. Janus activated kinases (JAK) phosphorylate STAT3 in response to stimulation by cytokines or growth factors. The STAT3 signaling pathway has been validated as a promising target for development of anticancer therapeutics. Small-molecule inhibitors of JAK/STAT3 signaling represent potential molecular-targeted cancer therapeutic agents. In this study, we investigated the role of JAK/STAT3 signaling in 6-bromoindirubin-3'-oxime (6BIO)-mediated growth inhibition of human melanoma cells and assessed 6BIO as a potential anticancer drug candidate. We found that 6BIO is a pan-JAK inhibitor that induces apoptosis of human melanoma cells. 6BIO directly inhibited JAK-family kinase activity, both in vitro and in cancer cells. Apoptosis of human melanoma cells induced by 6BIO was associated with reduced phosphorylation of JAKs and STAT3 in both dose- and time-dependent manners. Consistent with inhibition of STAT3 signaling, expression of the antiapoptotic protein Mcl-1 was downregulated. In contrast to the decreased levels of phosphorylation of JAKs and STAT3, phosphorylation levels of the Akt and mitogen-activated protein kinase (MAPK) signaling proteins were not inhibited in cells treated with 6BIO. Importantly, 6BIO suppressed tumor growth in vivo with low toxicity in a mouse xenograft model of melanoma. Taken together, these results show that 6BIO is a novel pan-JAK inhibitor that can selectively inhibit STAT3 signaling and induces tumor cell apoptosis. Our findings support further development of 6BIO as a potential anticancer therapeutic agent that targets JAK/STAT3 signaling in tumor cells.

Synthesis and antiproliferative activity of 7-azaindirubin-3'-oxime, a 7-aza isostere of the natural indirubin pharmacophore

The bis-indole alkaloid indirubin and its analogues bear a very interesting natural pharmacophore. They are recognized mainly as kinase inhibitors, but several other activities make them possible candidates for preclinical studies. Based on the previously reported activity of 7-bromoindirubin-3'-oxime and its derivatives, the synthesis of indirubins bearing a heterocyclic nitrogen atom at position 7 was carried out. Herein, we report the first synthesis of 7-azaindirubin-3'-oxime (12) as well as its antiproliferative activity against 57 cancer cell lines and its inhibitory activity against a series of kinases. 7-Azaindirubin (10) and its 3'-oxime derivative (12) showed reduced activity as kinase inhibitors in comparison with other known indirubin derivatives, but antiproliferative activity with a best GI(50) value of 0.77 microM.

Cutting edge: Necrosis activates the NLRP3 inflammasome

Cells undergoing necrosis release endogenous danger signals that possess proinflammatory potential. In this study we show that mature IL-1beta and IL-18 are released by necrotic cells but not by apoptotic cells. We identify 7-bromoindirubin-3'-oxime, an indirubin oxime derivative that induces necrosis, as a potent inducer of caspase-1 activation and release of mature IL-1beta and IL-18. Inflammasome activation was triggered by other necrosis-inducing treatments but was not observed in response to apoptosis-inducing stimuli. Necrosis-induced inflammasome activation was mediated by the NLRP3 and ASC molecules. Release of IL-18 and IL-1beta in response to necrosis-inducing stimuli was observed in THP-1 macrophages and the MSTO-211H human mesothelioma cell line independently of LPS priming. Using the in vivo model of naphthalene-induced airway epithelial cell injury, we showed that necrosis activates the ASC inflammasome in vivo. Our study identifies a new mechanism through which necrosis generates proinflammatory molecules that contributes to the sterile inflammatory response.